Behavioural switching mechanism of crayfish avoidance reaction after establishment of social hierarchy

当小龙虾处于休息姿势时，机械刺激引起回避反应，反应模式根据小龙虾的大小由飞镖反应转变为转向反应。此外，当两只以前不认识的小龙虾相遇时，立即发生打斗，并在几次接触中确定了主从关系。我在这个研究中已经证明，小龙虾之前在对尾扇的机械刺激下表现出飞镖反应，当它们赢得与对手的战斗后，它们的回避反应的表现发生了变化。在打斗前，它们主要表现出飞镖反应（约占47只小龙虾的92%），而接触尾扇主要引起转弯反应（94%）。统计分析显示，优势小龙虾在打斗前后的镖反应和转身反应发生概率差异有统计学意义（p<0.0001：配对t检验）。在打斗之后，通常观察到更整齐的动物会从占主导地位的小龙虾面前逃跑。下级小龙虾对机械刺激的反应基本一致。47只动物在打斗前（95%）和打斗后（91%）接触外凸体主要引起飞镖反应。为了表征优势小龙虾回避反应的行为变化，连续测试了优势小龙虾对感官刺激的反应。第一组将优势、从属小龙虾继续配对8 d。半数以上的部下在5天内被优势小龙虾杀死。当施加机械刺激时，优势体一直倾向于表现出转弯响应。第1天试验结束后立即将第二组优势小龙虾与从属小龙虾分离。随着时间的推移，出现转弯响应的概率减小，出现飞镖响应的概率增大。第2天和第3天发生转弯反应的概率仍高于dart反应的概率。第4天的回合反应和省道反应之间没有明显的偏好，从第5天开始省道反应的释放频率增加。第三组测试结束后将主、从属小龙虾分开，从第二天开始将两组小龙虾配对1小时。占主导地位的小龙虾即使在第8天也继续表现出轮流反应。这表明，与下属的接触是保持回避反应行为转变的必要条件。少

When the crayfish showed resting posture, mechanical stimulation to the tailfan elicited avoidance reaction in which response pattern was changed from dart to turn response according to the size of the crayfish. Furthermore, when two previously unacquainted crayfish encounter, fighting occurred immediately and dominant-subordinate relationship was determined within several contacts.I have shown in this study that small crayfish that previously showed dart response in response to mechanical stimulation to the tailfan changed their performance of avoidance reaction when they won the fights with opponents. While they mainly showed dart response (about 92% from 47 crayfish) before fighting, the touching tailfan predominantly elicited turn response (94%). Statistical analysis showed the occurrence probability of the dart response as well as that of the turn response was significantly different between dominant crayfish before and after fighting (p<0.0001: paired t test). After fighting, sub … More ordinate animals were usually observed to run away from the approach of dominant crayfish. The response of the subordinate crayfish to the mechanical stimulation was almost consistent. Touching of the exopodite mainly elicited dart response before (95% from 47 animals) and after (91%) fighting.To characterize behavioral change of the avoidance reaction in the dominant crayfish, the response of them to the sensory stimulation was continuously tested with 3 different groups. In the 1st group, the dominant and subordinate crayfish were kept to pair for further 8 days. More than half of the subordinates were killed by dominant crayfish within 5 days. Dominant continuously preferred to perform the turn response when the mechanical stimulation was applied. Dominant crayfish of the 2nd group were re-isolated from the subordinates immediately after the test of the 1st day. As days have passed, the probability of the occurrence of the turn response was decreased and that of dart response was increased. Occurrence probability of turn response was still statistically higher than that of dart response in the 2nd and 3rd day. There was no significant preference between turn and dart response in the 4th day, and the dart response was released more often from the 5th day. In the 3rd group, the dominant and subordinate crayfish were separated after the test but both crayfish were paired together for 1 hour from next day. The dominant, crayfish continue to show turn response even in the 8th day. These suggested contact with subordinate is needed to keep the behavioral transition of avoidance reaction. Less